What is this plug on 4R75W?
 

I've been trying to track down a leak on my 2004 with a 4R75W. I have changed the pan gasket (which was very rigid and inflexible) and cleaned up the pan mating surfaces. That fixed a lot of the issues but I still have a leak somewhere. There's a plug on the side of the transmission (see picture) that showed signs of weeping while the truck was running. (The picture is a 4R70W but it's the same plug). What is it for? Do I just tighten it or apply teflon tape? Any information is much appreciated!

Attachment 38554

That gasket you repaced is most likely a permanent type gasket. I know my 4R70Ws have that gasket and I never change it. Don't transmissions have vents? Maybe you have a clogged vent or something like that.

Yes I was aware that the gasket was reusable but it was 13 years old and brittle as hell. I feel much better with the new one I put in there. The pan had never been off, still had the yellow plug laying in there. I just don't what that plug in the picture is for. Any diagrams or schematics around?

Thats the line pressure test port

D

Awesome. Should I just snug it down then?

It's odd that it's leaking. Be careful as that is a tapered plug in an aluminum housing.

IF its actually what is leaking then this is one place i would consider using RTV on a transmission. Again, IF it is the leak source then I think I would remove it, clean the threads up and very lightly coat it with RTV before reinstalling it. Keepig in mind that I'm installing a tapered plug into a weak cast aluminum housing.

D

What about teflon tape?

With the truck running, I got under the truck and wiped around the area and saw transmission fluid reappearing at the bottom of the plug. So I'm positive this is the problem area. I like the rtv idea, should I bottom out the plug or do you happen to know of a torque spec? Thanks for the help.

I'm not Darrin, but I think I'd use teflon tape before I'd use RTV. Clean the threads on the plug and in the hole thoroughly. I'd also check the housing in that area carefully for cracks.

Awesome, thanks!

Several reasons not to use teflon tape with stuff like this. Particularly on transmissions and specifically where you are putting a tapered plug into a straight, brittle cast aluminum housing that is prone to cracking. Most I have seen split had teflon tape on them.

RTV, and not much of it.

D

Thank you for correcting me, Darrin. You are the transmission expert, I'm not.

Well I used one layer of teflon (didn't see the most recent responses) and the bolt tightened down properly. No more leak! If I have another issue, I'll pull it out and use RTV. Thanks again for all the help.

It'll be fine.

D

Hey you still on this forum??